The Role of Chemical Composition in Determining the Charge‐Carrier Dynamics in (AgI)x(BiI3)y Rudorffites

Abstract Silver‐bismuth‐based perovskite‐inspired materials (PIMs) are increasingly being explored as non‐toxic materials in photovoltaic applications. However, many of these materials exhibit an ultrafast localization of photogenerated charge carriers that is detrimental for charge‐carrier extraction. In this work, such localization processes are explored for thermally evaporated thin films of compositions lying along the (AgI)_x(BiI₃)_y series, namely BiI₃, AgBi₂I₇, AgBiI₄, Ag₂BiI₅, Ag₃BiI₆, and AgI, to investigate the impact of changing Ag⁺/Bi³⁺ content. A persistent presence of ultrafast charge‐carrier localization in all mixed compositions and BiI₃, together with unusually broad photoluminescence spectra, reveal that eliminating silver will not suppress the emergence of a localized state. A weak change in electronic bandgap and charge‐carrier mobility reveals the resilience of the electronic band structure upon modifications in the Ag⁺/Bi³⁺ composition of the mixed‐metal rudorffites. Instead, chemical composition impacts the charge‐carrier dynamics indirectly via structural alterations: Ag‐deficient compositions demonstrate stronger charge‐carrier localization most likely because a higher density of vacant sites in the cationic sublattice imparts enhanced lattice softness. Unraveling such delicate interplay between chemical composition, crystal structure, and charge‐carrier dynamics in (AgI)_x(BiI₃)_y rudorffites provides crucial insights for developing a material‐by‐design approach in the quest for highly efficient Bi‐based PIMs.